In Texas, there is a mandatory 60 day waiting period between the time you file for divorce and the time you finalize it. So, the shortest divorce in Texas is going to be 61 days. To complete your divorce in the shortest possible time, you'll want to start working on the details of your divorce immediately after filing. If you're using the No Nonsense™ Divorce Workbook, you and your spouse should start completing it right after the Original Petition for Divorce is filed.
Once you and your spouse have made decisions on all of the details of your divorce, the Final Decree of Divorce will need to be drafted, reviewed and signed. If you can finish all of that before the waiting period is up, then you'll be ready to finalize the divorce soon after the 60 days have elapsed.
Just to clarify, the 60 days is a waiting period - not a deadline. You can certainly take longer than 60 days, you just can't take less than 60 days.
If you take more than a year to complete your divorce, it may get dismissed if nothing appears to be happening.